1. Field of the Invention
The present invention relates to a radio frequency coil for a magnetic resonance imaging apparatus, which transmits and receives a magnetic resonance signal for forming a magnetic resonance image of a human body in a magnetic resonance imaging apparatus being a medical diagnosis device for understanding the internal structure of a human body.
2. Description of Related Art
As a tomographic method for understanding the internal structure of a human body, there is X-ray computerized tomography (C.T.) using X-rays and magnetic resonance imaging (MRI) using the magnetic resonance signal of an element in a human body. The tomograph using a magnetic resonance (MR) phenomenon has several advantages compared to the X-ray C.T. That is, a magnetic field absolutely harmless to human bodies is used in the MRI method, so long imaging times or frequent examining does no harm to a human body. Also, discrimination of molecules which is not made in the X-ray tomography is possible. Furthermore, a two-dimensional or three-dimensional tomographic image can be obtained at an arbitrary place in an arbitrary direction on X, Y and Z axes. Because of these merits, the MRI has become an indispensable piece of medical imaging equipment.
The MRI apparatus is roughly comprised of a main magnet, coils and a scan processor. The main magnet for forming a strong magnetic field is a permanent magnet, an electromagnet, or a superconducting magnet using a superconductive body whose magnetic field intensity is typically between 0.2 Tesla and 2.0 Tesla (1 Tesla is 10000 gauss magnetic field). Comprising the coil are a gradient magnetic field coil, for making a gradient magnetic field of directions X, Y and Z; a transmit radio frequency coil for making a magnetic resonance (MR) signal by applying energy to an atomic nucleus spin of a human body; and a receive radio frequency coil for receiving a magnetic resonance (MR) signal emitted from a human body. The scan processor includes a spectrometer for demodulating and greatly amplifying a received magnetic resonance signal, a controller for controlling the operation of each coil, and a processor for converting a received analog signal into digital data and performing a Fourier transformation from frequency data to data on planes X and Y.
In the magnetic resonance imaging apparatus structured as above, in the case that a magnet for forming a vertical-direction magnetic field, having a low magnetic field of 0.5 tesla or less, is used as a coil for receiving a magnetic resonance signal emitted from a human body, it is common to use a solenoid coil. FIG. 1 shows a conventional 3-turn coil as the above-described solenoid coil. The case of carrying out an operation simultaneously with taking a magnetic resonance image is becoming more common. Since the turns of the conventional radio frequency coil shown in FIG. 1 are disposed at equal intervals, it is difficult to gain access to the diseased part of a human body within the radio frequency coil to operate thereon, or to observe the diseased part. Also, patient's eyes are closed when the patient's head is examined, so the patient feels uncomfortable. FIG. 2 shows a human's head within a receive radio frequency coil during head examining. As shown in FIG. 2, no problem occurs when an operation is performed near the upper opening of the radio frequency coil. However, in case that an operation is carried out on the other portions of the radio frequency coil, access is obstructed by the coil. Thus, it is difficult to obtain a magnetic resonance image simultaneously with conducting an operation.